Almaani N, Hussein H, Abdaljaleel M
… +1 more, Alsoud K
Am J Dermatopathol
· 2026 Jun · PMID 42160684
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Lymphangioma-like Kaposi sarcoma (LLKS) is a rare histologic variant of Kaposi sarcoma that can closely mimic benign vascular proliferations, posing a diagnostic challenge-especially in immunocompetent individuals. We re...Lymphangioma-like Kaposi sarcoma (LLKS) is a rare histologic variant of Kaposi sarcoma that can closely mimic benign vascular proliferations, posing a diagnostic challenge-especially in immunocompetent individuals. We report a case of LLKS in an HIV-negative elderly man who presented with unilateral, sporotrichoid violaceous papules and plaques confined to the upper limb. Histopathologic examination demonstrated irregularly dilated vascular channels with positive immunostaining for human herpesvirus 8 (HHV-8). This case underscores the importance of considering LLKS in the differential diagnosis of vascular-appearing lesions in immunocompetent patients with atypical clinical presentations.
Makhija M, Robinson J, Van Vliet C
… +1 more, Wood BA
Am J Dermatopathol
· 2026 Jun · PMID 42160681
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Indeterminate dendritic cell tumour (IDCT) is a rare form of non-Langerhans cell histiocytosis which typically presents with skin lesions. The histological appearances resemble Langerhans cell histiocytosis, although the...Indeterminate dendritic cell tumour (IDCT) is a rare form of non-Langerhans cell histiocytosis which typically presents with skin lesions. The histological appearances resemble Langerhans cell histiocytosis, although the cells are negative for CD207 (langerin) and lack Birbeck granules. The molecular mechanisms are diverse and include a subset of cases associated with ETV3::NCOA2 fusion. A significant minority of cases are associated with underlying haematological neoplasms, which require clinical exclusion.
Am J Dermatopathol
· 2026 Jun · PMID 42160677
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A 76-year-old man presented with a persistent pruritic eruption initially diagnosed as Grover disease, unresponsive to topical corticosteroids, and only partially responsive to systemic steroids. During the course of sev...A 76-year-old man presented with a persistent pruritic eruption initially diagnosed as Grover disease, unresponsive to topical corticosteroids, and only partially responsive to systemic steroids. During the course of several months, serial skin biopsies revealed spongiotic dermatitis with increasing eosinophilic infiltration. Despite negative serologic testing for syphilis and Lyme disease, a spirochete stain later showed slender filamentous organisms, prompting further investigation. Repeated serologies, including dilution to rule out the prozone phenomenon, remained negative. A panel of dermatopathologists re-reviewed the biopsies and raised concern for specimen contamination. The patient's final diagnosis was an idiopathic dermal hypersensitivity reaction, now improving with methotrexate. This case highlights the diagnostic challenges associated with false-positive and false-negative results in Treponema pallidum immunohistochemistry staining and syphilis serologic testing. We review the limitations and pitfalls of immunohistochemistry staining, serologic assays, and nucleic acid testing for syphilis, including cross-reactivity, contamination, and the prozone effect. Awareness of these diagnostic limitations is essential, because of misdiagnosis of syphilis can have significant clinical and public health implications.
Am J Dermatopathol
· 2026 Jun · PMID 42160676
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Epithelioid fibrous histiocytoma (EFH) is a rare condition historically considered a morphologic variant of benign fibrous histiocytoma. However, recent molecular studies have shown that EFH is characterized by anaplasti...Epithelioid fibrous histiocytoma (EFH) is a rare condition historically considered a morphologic variant of benign fibrous histiocytoma. However, recent molecular studies have shown that EFH is characterized by anaplastic lymphoma kinase gene rearrangements, which are absent in benign fibrous histiocytoma. In this case report, we describe a case of EFH in a young woman, which presented a histopathologic diagnostic challenge due to an exuberant giant cell proliferation with intervening monocytic cells, a feature not typically seen in EFH. Molecular workup revealed an anaplastic lymphoma kinase rearrangement, allowing for a diagnosis of EFH to be made.
Am J Dermatopathol
· 2026 Jun · PMID 42160675
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Cutaneous metastasis (CM) is a rare manifestation of internal malignancy. We analyzed the incidence, clinical features, and patterns of metastatic spread among 408 CMs from 15 primary sites, excluding skin, breast, lung,...Cutaneous metastasis (CM) is a rare manifestation of internal malignancy. We analyzed the incidence, clinical features, and patterns of metastatic spread among 408 CMs from 15 primary sites, excluding skin, breast, lung, colorectum, and hematolymphoid primary sites, in a 34-year (1990-2024) single-institution retrospective review (88 cases) and literature review (320 cases). CMs from thyroid were most common in the single-institution review. A young median age was observed in patients with CMs from soft tissue (14 years) and bone (32 years) tumors. Male predilection was most observed in CMs from esophagus, mesothelium, and kidney. CMs from 9 of 15 primary sites favored the head and neck region. CMs most presented as solitary lesions from bile duct (72%), thyroid (69%), and pancreas (67%) primary sites. In total, 45% of CMs from the bile duct were due to catheter-related tumor seeding. The primary sites with the highest percentage of CMs at initial presentation were neuroendocrine (55%), esophagus (45%), and pancreas (40%). The time interval between primary cancer diagnosis and development of CM ranged from 0 to 429 months. The shortest median time interval was observed in CMs arising from pancreas (1 month) and esophagus (2 months), while the longest median time interval was observed in those from prostate (80 months) and kidney (46 months). In summary, CM may be the initial clinical presentation of underlying malignancy from uncommon primary sites and can exhibit distinctive patterns of cutaneous spread based on the primary cancer type and anatomic location.
The application of molecular techniques has significantly refined the classification of cutaneous mesenchymal tumors, uncovering recurrent genetic alterations that aid in diagnostically challenging cases. Dermatofibroma,...The application of molecular techniques has significantly refined the classification of cutaneous mesenchymal tumors, uncovering recurrent genetic alterations that aid in diagnostically challenging cases. Dermatofibroma, or cutaneous fibrous histiocytoma, is a common benign neoplasm with broad morphologic variability and limited immunohistochemical specificity, for which recurrent protein kinase C gene fusions have recently been described. We report a novel case of a cellular, pseudoangiomatous DF arising on the dorsum of a 56-year-old man and harboring an in-frame MYADM::PRKCG fusion transcript. Histologically, the lesion displayed high cellularity and prominent vascularity, and focal smooth muscle actin and desmin positivity, initially suggesting angiomatoid fibrous histiocytoma. Targeted RNA sequencing identified a previously unreported MYADM::PRKCG fusion, enabling definitive classification. This is the first description of a MYADM::PRKCG rearrangement in DF, further expanding our knowledge about the molecular landscape of this neoplasm.
Cutaneous pseudolymphoma is a benign reactive process that comprises a heterogeneous group of entities that resembles lymphoma clinically and/or histologically. This condition can be idiopathic or caused by drugs, infect...Cutaneous pseudolymphoma is a benign reactive process that comprises a heterogeneous group of entities that resembles lymphoma clinically and/or histologically. This condition can be idiopathic or caused by drugs, infections, or foreign agents. Cutaneous pseudolymphoma could belong to the B-cell type, the T-cell type, or be mixed. The multiple presentations raise a significant diagnostic challenge and require clinicopathologic correlation and follow-up. This case report presents the clinical, histopathologic, immunophenotypic, and genetic findings of a cutaneous T-cell lymphoma-like eruption from trimethoprim-sulfamethoxazole in a 55-year-old female systemic lupus patient.